The present invention relates to grand pianos and, more particularly, to apparatus useful in association with such pianos for adjusting the hammer strike line in relation to the piano strings.
A grand piano conventionally comprises a plurality of keys each operatively connected through a suitable action mechanism to a hammer disposed for striking a respective piano string in response to depression of the associated key. It is known that the precise points along the strings which are struck by the hammers, collectively defining the hammer strike line, upon the playing of the keys are critical to the production of brilliant and properly sounding notes. In this regard, the strike points of the strings forming the treble end of the keyboard are of particular concern in that these relatively short length strings are highly sensitive to changes in hammer strike points. Thus, a very small change in the strike point of a treble string, say, for example, about one-third of a centimeter, can result in a significant detuning of the string. Such strike point changes may result from, inter alia, environmental conditions, such as humidity and the like, which cause portions of the action mechanism or hammer to expand or contract and thereby alter the string strike points. While the sounds produced by the longer length bass strings are not affected as extremely as are the treble strings by changes in strike points, they too may nevertheless produce a less than optimum sound especially if a rather large change is experienced.
In the past, strike line adjustments have been largely effected on a trial and error basis wherein a technician physically adjusts the position of the piano key frame assembly, which assembly carries all of the keys together with their associated action mechanisms and hammers, while simultaneously listening to the sound produced by the highest pitched note on the keyboard. Upon properly establishing the strike point for this latter note, it is then assumed that the strike points of the remaining strings have also been properly established.
In order to facilitate the foregoing, various devices have been proposed to aid the technician in making the slight longitudinal adjustments in the position of the key frame assembly necessary to optimumly set the strike line for obtaining the best sound from the high treble portion of the keyboard. These prior art devices typically include an adjustment screw journalled through the piano key block disposed adjacent the treble end of the keyboard for operating a member receiving a suitable key frame shift pin. The key frame shift pin is rigidly secured to the key frame assembly such that operation of the adjustment screw is effective for longitudinally shifting the position of the key frame assembly to set the strike line as desired.
As noted above, the prior art adjustment screw is journalled through the piano key block such that its operative end is exposed for conveniently allowing adjustments to be made without requiring any disassembly of the piano. Although this feature is desirable when exercised by a properly trained technician, it is also subject to certain abuses from the untrained layman. In particular, either intentional or inadvertent operation of the adjustment screw by an untrained layman may result in the hammer strike line being moved to an extent totally degrading the sound normally produced by the piano. In addition, the key block itself being comprised of wood is subject to various environmental conditions which may warp or otherwise alter the characteristics of the assembly. This would, in turn, slightly change the position of the key frame shift pin and thereby adversely affect the previously established hammer strike line. Also, repeated operation of the adjustment screw tends to adversely affect the nature of the key block channel through which the screw passes. Thus, after repeated use, the adjustment screw may begin to slightly slip within the key block channel making it difficult to effect a desired adjustment as well as difficult to securely maintain a previously set adjustment.